CronParser

A python script to expand values of cron time string. The script will output different values allowed for each time component in the console.

Command to Execute

python3 <file_name> <cron_string>

1. The file name to execute in this project is main.py
2. cron string should be a valid string enclosed by inverted commas. The validity of a cron string is described in details below.
3. Test Cases can be run using this command: python3 -m unittest test.py

Example of a valid command string: python3 main.py '*/15 0 1,15 * 1-5 /usr/bin/find'

Supported Time Components

The cron string takes input of six values separate by space.

eg: */15 0 1,15 * 1-5 /usr/bin/find

Below are the details of each part in cron string in sequence:

1. Minutes: Values supported are from 0 to 59 integer values
2. Hours: Values supported are from 0 to 23 integer values
3. Day of Month: Values supported are from 1 to 31 integer values
4. Month: Values supported are from 1 to 12 integrer values representing month in a calender year. January and December are represented by 1 & 12 respectively. Also, string values for month are also supported. Valid string values are JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
5. Day of week: Values supported are from 1 to 7 integer value representing different day in a week. Sunday and Saturday are represented by 1 and 7 respectively. All other week days are represented by integer in the same order eg: Monday by 2, Tuesday by 3, Wednesday by 4 etc. Also, string values for week day are also supported. Valid string values are SUN MON TUE WED THU FRI SAT
6. Command: It represents a string value of path of command to be executed by cron.

Supported Special Characters and Usages

1. * : Astrisk represent all values for a time component. “*” in the minute field means every minute.
2. / : Slash represents increments. “0/15” in the seconds field means the seconds 0, 15, 30 and 45. Only numerical values are allowed before and after slash. eg: "1/20", "10/45" etc.
3. - : A hyphen indicates a range. “15-18” in the hour field means the hours 15, 16, 17 and 18. Only numerical values are allowed before and after hyphen. eg: "1-20", "10-45" etc.
4. , : A comma is used to separate multiple allowed values. “MON,WED,FRI” in the day_of_week field means the days Monday, Wednesday, and Friday.

Project Design Considerations:

1. The main.py file is the main executor of the project.
2. ExpressionParser class is the driver class
3. TimeComponent class is parent class which is inherited by other specific time bound class. This class has methods to parse an expression in a particular time format.
4. MinuteComponent, HourComponent, DayOfMonthComponent, MonthComponent and DayOfComponent inherits TimeComponent class. All details and static values are contained in respective child class.
5. CommandComponent class is an independent class.
6. Baisc validation for cron expression are also implemented in TimeComponent class.

Example Command:

python3 main.py '*/15 0 1,15 * 1-5 /usr/bin/find'

Output: Expression: */15 0 1,15 * 1-5 /usr/bin/find Minute 0, 15, 30, 45 Hour 0 DayOfMonth 1, 15 Month 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 DayOfWeek 1, 2, 3, 4, 5 Command /usr/bin/find